In a general photolithographic technique for manufacturing semiconductor devices, a photoresist is applied to a substrate, such as a semiconductor wafer or an FPD substrate. A resist film thus formed is then exposed with a predetermined circuit pattern, and the exposed pattern is developed so that the circuit pattern is formed in the resist film.
In such a photolithographic process, bubbles of nitrogen gas and particles (foreign matters) may come to be mixed in a processing liquid, such as a resist liquid and a developer to be supplied to a substrate, for various reasons. When a processing liquid containing bubbles and/or particles is supplied to a substrate, coating may be non-uniform and/or a defect may occur. Thus, a processing liquid supplying apparatus, which applies a processing liquid to a substrate, is provided with a filter for removing bubbles and particles contained in the processing liquid by filtration.
There is known a processing liquid supplying apparatus including a plurality of filters which serve as an apparatus for improving an efficiency for filtering bubbles and particles contained in a processing liquid. The processing liquid supplying apparatus supplies, to a wafer or the like, a processing liquid having been passed through these filters. If a plurality of filters are installed in a processing liquid supplying apparatus, it becomes larger and must be modified drastically.
JP2011-238666A (see the claims and FIG. 7) discloses a chemical liquid supplying system of a circulating filtration type, including: a first container for storing a chemical liquid (processing liquid); a second container for storing the chemical liquid; a first pump disposed on a first pipeline connecting the first container and the second container to feed the chemical liquid stored in the first container toward the second container; a first filter disposed in the first pipeline; a second pipeline connecting the first container and the second container; and a second pump disposed on the second pipeline to feed the chemical liquid stored in the second container toward the first container.
WO2006/057345 (see the claims and FIG. 4) discloses another processing liquid supplying apparatus of a circulating filtration type provided with a single filter. The apparatus includes: a buffer container for a photoresist liquid (processing liquid); a circulating filtration device that draws a part of the photoresist liquid from the buffer container to filtrate the same, and then returns the filtered photoresist liquid to the buffer container; and a piping for sending the photoresist liquid from the buffer container or the circulating filtration device to a photoresist coating device. JP2001-77015A discloses an arrangement in which pumps are respectively disposed on the primary side and the secondary side of a filter.
In the processing liquid supplying apparatuses disclosed in JP2011-238666A and WO2006/057345, the chemical liquid (processing liquid) having been filtered by the filter(s) is returned to the first container (buffer container), and the chemical liquid returned to the first container is ejected to a wafer. In order to improve the chemical-liquid filtration efficiency, it is necessary to further circulate the chemical liquid once returned to the first container so as to filtrate the chemical liquid plural times. It elongates the standby time and lowers the throughput of the apparatus.
With the recent improved resolution of particle inspection apparatuses and pattern inspection apparatuses, particles of a currently negligible size in a processing liquid would be found to be problematic in the future. By taking measures for removing such micro particles, a throughput of semiconductor devices can be enhanced. Thus, a processing liquid supplying system is more and more required to have measures for restraining particles. For example, dust generated from a pump in a processing liquid supplying passage cannot be ignored any more.